Lithium hydroxide doped tris(8-hydroxyquinoline) aluminum as an effective interfacial layer in inverted bottom-emission organic light-emitting diodes

Lithium hydroxide doped tris(8-hydroxyquinoline) aluminum (Alq₃:LiOH) is used as an effective interfacial layer for the fabrication of efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs). When 15% LiOH was doped into an Alq₃ electron-transporting layer, the device properties such as the turn-on voltage, maximum luminance, and device efficiency improved, becoming better than those obtained with LiF doping and comparable to those of β-naphthylphenylbiphenyl diamine (NPB)/Alq₃-based OLEDs with conventional geometry. Electrical analysis reveals that LiOH-doped Alq₃ layers have an enhanced electron injection and transport ability. X-ray and ultraviolet photoelectron spectroscopy results clearly show that the dipole layer formed at the indium tin oxide (ITO)/organic interface contributed to the reduction of the ITO work function, resulting in a decrease of the electron injection barrier. The enhanced electron injection and transport efficiency improves the charge carrier balance in IBOLEDs and leads to better device efficiency. Furthermore, improved morphology of the organic layer can be obtained by doping LiOH into Alq₃, which improves device operational stability under thermal stress. - Highlights: • Inverted bottom-emission organic light-emitting diodes with Alq₃:LiOH interfacial layer were investigated. • Alq₃:LiOH layers possess an enhanced electron injection and transporting ability. • The dipole layer is formed at the Alq₃:LiOH/indium tin oxide interface. • Alq₃:LiOH interfacial layer stabilizes the surface morphology of the Alq₃ film